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Chapter 22: Descent with Modification: A Darwinian View of Life
As you study this chapter, read several paragraphs at a time to catch the flow of ideas and understand the reasoning that is being described. In some places, the text describes a narrative or story of events that led to Darwin’s theory of evolution. Therefore, first read the narrative to absorb the big picture and then return to answer the few questions that accompany this material.
Overview (p.414)
1. Define evolution broadly, as discussed in the overview.
2. State 3 questions you have about evolution before reading the rest of the chapter.
The Darwinian revolution challenged the traditional view of a young Earth inhabited by unchanging species. (p.414-419)
This section takes a look at the historical setting and influences on Darwin. It is interesting reading and puts Darwin in a historical context, but is not required knowledge for the redesigned AP Biology exam. The one thing you should get from this section is Lamark’s explanation for the mechanism for evolution. It is important that you are able to compare this view of evolution, along with others, to the current theory of evolution based on Darwin’s findings.
3. Explain Lamark’s theory of inheritance of acquired characteristics. Why was Lamark wrong?
Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life. (p.419-422)
4. Charles Darwin proposed that the mechanism of evolution is natural selection and that it explains how adaptations arise. What are adaptations? Give two examples of adaptations. 5. Explain the process of natural selection.
6. Let’s try to summarize Darwin’s observations that drive changes in species over time:
Observation Cite an Example 1. Variations in traits exist.
2. These variations (traits) are heritable.
3. Species overproduce.
4. There is competition for resources; not all offspring survive.
7. From these four observations, what two inferences did Darwin make?
8. It is important to remember that differences in heritable traits can lead to differential reproductive success. This means that the individuals who have the necessary traits to promote survival in the current environment will leave the most offspring. How can this differential reproductive success affect the match between organisms and their environment?
9. To demonstrate your understanding of this section, complete the following sentences:
______do not evolve. ______evolve.
Now, take out your highlighter and mark the information in the box above . Hold these ideas firmly in your brain! Finally, if you are ever asked to explain Darwin’s theory of evolution by natural selection (a common AP essay question), do not pull out the phrase “survival of the fittest.” Instead, cite the points made in question 11 and explain the inferences that are drawn from them.
Evolution is supported by an overwhelming amount of scientific evidence. (p.423-425) For the following questions, you are going to have to research answers on the Internet. Put all explanations and answers in your own words. Be as descriptive as possible when answering the questions.
10. MRSA is becoming increasingly more common. What is it?
11. How did it become so dangerous? Explain the evolution of MRSA’s resistance to methicillin.
12. Do antibiotics cause bacteria to become resistant? Explain your response.
13. Let’s make a list of the four evidences for evolution that are described in this concept section. Give an example of each.
Evidence for Evolution Example
14. How does the fossil record give evidence for evolution? 15. What is meant by each of the following terms? Give an example of each.
Term Explanation/Example Homologous structures
Vestigial structures
Analogous structures (see p. 476-477)
16. How do homologous structures give evidence for evolution?
****Answer the “Challenge Question” on page 427 in full, complete sentences. You must state evidence that supports your answer. Complete answers should not just state the answer, or what you know, but should explain HOW you know what you know!
Study Tip Homologous structures show evidence of relatedness (whale fin, bat wing).
Analogous structures are similar solutions to similar problems but do not indicate close relatedness (bird wing, butterfly wing).
Let’s wrap up all of these ideas with a final summary.
ORGANIZE YOUR THOUGHTS
1. Evolution is change in species over time. 2. Heritable variations exist within a population. 3. These variations can result in differential reproductive success. 4. Over generations, this can result in changes in the genetic composition of the population.
And remember: Individuals do not evolve! Populations evolve.
Answer the “Challenge Question” on page 427 in full, complete sentences. You must state evidence that supports your answer. Complete answers should not just state the answer, or what you know, but should explain HOW you know what you know!